1. Field of the Invention
The present invention generally relates to force distribution arrangements and, more particularly, to an arrangement for distributing a force from a single point to multiple points such that equal forces are applied to each of the multiple points.
2. Description of the Prior Art
In the construction of electrical devices, the structures for assembling circuit elements into functional groups and the packaging and structural support of such functional groups of circuit elements often constitutes a major portion of the cost of a manufactured electronic device or component therefor. With increased complexity of individual circuit elements and manufactured devices, in general, has come an increased complexity of interconnection structures such as printed circuit boards using, for instance, epoxy and fiberglass substrates. Increased circuit element density as well as integration density has increased heat tolerance and dissipation requirements of these interconnection elements as well as the use of multi-layer boards.
A high-performance structure now in widespread use is the multi-layer ceramic (MLC) type of interconnection structure, described in U.S. Pat. No. 4,245,273. In these structures, a potentially differing interconnection pattern is formed on each of a multiplicity of layers of ceramic substrate. These interconnection patterns include perforations, known as vias, in the ceramic carriers which are selectively filled with conductive paste and provide electrical continuity between layers of the MLC structure. The respective layers are then stacked and sintered under pressure and high temperature to provide a unitary structure with many interconnection lamina embedded therein to allow formation of electronic interconnection structures of high connection complexity.
The sintering process is fairly time-consuming due to the necessity of bringing the MLC assembly to a predetermined temperature near the melting point of the material throughout its volume for the sintering process to properly proceed without distortion of the lamina or the interconnection material. Therefore, it is desirable to perform the sintering process on a number of MLC structures at the same time.
While it may be that the sintering process will be done of a plurality of stacks of layers where each stack contains the same number of layers, this may not always be the case. Therefore, the stacks may not all be of equal height. Further, possible variations in coating thickness of the interconnection patterns on each of the layers may alter the respective heights of the different stacks.
For this reason, sintering of a plurality of stacks of MLC layers cannot be done in a single press without plural platens and some type of gimballing arrangement to accommodate differing stack heights. While some gimballing arrangements are known in other arts, such as in clamps, known gimballing arrangements do not provide for accurate force equalization or maintaining applied forces centralized on the platens, which is essential to maintaining parallelism between the top and bottom surfaces of the stacks.
It should also be noted that for the sintering process to be conducted properly with ceramics of the type currently used in MLC structures, a pressure of approximately 500 g/cm.sup.2 is required. since MLC devices can be of any desired size and it is desired that the number of stacks to be concurrently sintered be at least as large as will provide production economies, both the amount of pressure applied to each platen and the sum of forces applied to all platens can become quite large. Therefore, the amount of force which must be carried by each element of any gimballing arrangement may also be quite large.
The sintering process depends upon both the temperature reached by the material or materials to be sintered and the mechanical pressure applied to the materials. Since, if a plurality of stacks are to be concurrently sintered, they will all be subjected to the same temperature, it is extremely important that they be subjected to the same pressure with a high degree of precision. While this could be done by individual application of controllable forces to each of the stacks, the desirability of minimizing the amount and volume of equipment which must be placed within the sintering furnace effectively precludes this approach. Further, such an approach would not inherently provide any equalization of the forces or provide for maintaining parallelism between the top and bottom surfaces of the stacks. Moreover, application of force from a single point to plural stacks is much to be preferred since it would be consistent with prior single platen apparatus and would provide for differing numbers of stacks by merely changing the apparatus for transferring this single force to the plurality of platens, should an acceptable arrangement with plural platens be available.
Therefore, in summary, the prior art has not addressed the problem of providing an arrangement which will simultaneously apply large and inherently equal forces derived from a single applied force with a high degree of precision to a plurality of stacks of differing heights while concurrently providing for the application of centered forces on the platens.
It is to be understood from the above summary of the background of the invention that the application of equal forces derived from a single force to a plurality of platens is particularly critical for the fabrication of MLC structures in view of the large forces involved, the criticality of the equality and centering of forces and the need to avoid inducing of dimensional distortion at high temperatures while accommodating thermally induced dimensional changes in the stacks. However, it is also to be understood that the invention is certainly not limited to such an application. On the contrary, it is to be understood that the invention is applicable to the imposition of forces of any magnitude to any regular or irregular surface or group of surfaces regardless of the criticality of any or all of the above concerns.